Rheostat



P 39, 19414 R. ABRAHAMsQN RHTBJUSTAT.

Filed July 27, 1940 2 sheets sheet l INVENTOR ROBERT ABRAHAMSON AM ATTORNEY Sept. 30, 1941 R. ABRAHAMSON 2,257,445

RHEOSTAT Filed July 2'7, 1940 2 Sheets-Sheet 2 INVENTOR ROBERT ABRAHAMSON BY W W M ATTORNEY Patented Sept. 30, 1941 UNITED STATES PATENT OFFICE 4 Claims.

' which the slider is more easily and more smoothly slidable even after long time of service.

It is a further object of the invention to provide as a novel article of manufacture an improved slider which may be installed in existing rheostats to improve the operation of the same.

Conventional rheostats are provided with a protective casing enclosing the resistance rod and the sliding bar for the slider, usually mounted above the resistance rod. The casing is provided with a slot through which the slider extends and I I which usually terminates in a finger operable knob or handle for moving the slider.

The conventional design of rheostats, as far as I am aware, is such that a force applied at the knob or handle of the slider will cause the slider to tilt with respect to the bar on which it slides. This tilting is highly undesirable for two reasons.

It may be assumed that an accurate adjustment of the rheostat is to be made according to the reading of a measuring instrument. This is done by moving the slider to a point on the resistor which will adjust the circuit for the proper resistance. Since, however, an applica tion of force at the knob or handle causes the slider to tilt, the adjustment of the rheostat to the predetermined point on the resistor will not be maintained after the knob or handle is released. At a movement of the slider in one direction or the other, the handle will tilt forward while the brushes lag behind a certain amount. Assuming now that the rheostat is adjusted to obtain the proper reading at the indicating instrument and the slider is then released, the slider will tilt back into its normal position whereby the brushes will move further in the direction in which the initial adjustment was made thereby causing unbalance of the adjusted circuit. This is an annoying property of the conventional rheostat well known to all persons working in electrical laboratories.

A further objectionable result of the tilting of the slider is the increased friction and oftentimes the jamming of the slider which occurs in rheostats which have been in service for sometime and in which the sliding bar has become oxidized or covered with dust due to moisture and impurities in the air.

It is thus an object of this invention to provide an improved rheostat in which the slider is easily movable and smoothly adjustable under all conditions.

According to the invention I provide a slider for a rheostat equipped with a protecting enclosure, the slider having a center portion through which the sliding bar passes, a neck portion eX- tending through the slot in the enclosure and a finger operable portion in the form of a pair of wings extending on either side from the neck portion down the sides of the center portion to a point below the center of the aperture, the wings being spaced from the sides of the center portion andsubstantially parallel thereto thereby overlapping the enclosure and providing at the lower ends of the wings a finger grip portion at which an applied force will be directed substantially through the axis of the sliding bar. If thus a force is applied at the finger grip portion, the slider will move but not tilt thereby permitting of easy and smooth adjustment even if sliding on a rod which is oxidized or covered with dust.

Further aims, objects and advantages of this invention will appear from a consideration of the description which follows with accompanying drawings showing for purely illustrative purposes an embodiment of this invention. It is to be understood, however, that the description is not to be taken in a limiting sense, the scope of the invention being defined in the appended claims.

Referring to the drawings:

Fig. 1 is a side elevation of a rheostat embodying the present invention, a part of the protecting enclosure being broken away to show the interior structure;

Fig. 2 is a front elevation of the rheostat shown in Fig. 1;

Fig. 3 is a side elevation partly in section of the novel slider of the rheostat of Figs. 1 and 2; and

Fig. 4 is a front elevation partly in section of the slider shown inFig. 3.

In the illustrated embodiment a resistance rod i0 is shown in the form 'of a substantially cylindrical ceramic body H wound with resistance wire E2. The rod is mounted between a pair of end supports I3 and [4 by means of a bolt (not shown) extending through the ceramic body and held in the end supports by means of nuts and I6. Terminals I1 and [8 are mounted to the end supports on insulating posts I9 and respectively and are connected to the ends of the resistance wire l2 by means of connecting bars 2| and 22 leading to clamps 23 and 24. The clamps fit tightly around the ceramic body and hold the ends of the windings of the resistance wire [2 in place.

A sliding contact is provided movable parallel to the resistance rod on a bar 25, the bar being secured to the end supports in insulating posts 26 and 21. In the illustrated embodiment the bar serves as a conductor to and from the sliding contact and is for this reason provided with a terminal 28.

The rheostat is equipped with an enclosure shown, in the illustrated embodiment, as including perforated cover plates 29 and 30 secured to the end supports I3 and I4 by means of screws 3! forming a protective casing therewith pre venting human contact with current conducting or heated parts of the rheostat. The cover plates 29 and 38 extend to a point above the sliding, bar to shield the same and form between themselves a narrow slot 32 preferably narrow enough to prevent human contact of the bar 25 therethrough.

Sliding contact is made with the resistance rod by means of a set of brushes 33 secured to a slider 34 by means of screws 35 and 36. The slider is shown on a larger scale in Figs. 3 and 4 and comprises a center portion 31 provided with an aperture 38 to accommodate the bar 25. A narrow neck portion 39 above the center portion connects the center portion with a finger operable portion which, in the illustrated embodiment. is shown in the form of a pair of wings 40 and 4!. The wings extend from the neck portion downwardly on either side and far enough as to provide a finger grip portion 42, 43 on both sides and in the same plane of the axis of the aperture 38 accommodating the bar 25.

Since in the illustrated embodiment the bar s rves as a conductor for the terminal 28 a con nection is established between the brushes 33 and the bar by means of a second set of brushes 44 mounted in the aperture 38 by means of the screws 35 and 36 and a threaded face plate 45.

Referring to the drawings of the assembled rheostat, Figs. 1 and 2, it is seen that the slider 34 extends with its neck portion 39 through the slot 32 in the enclosure. The finger operable portion 42, 43 is outside of the enclosure substantially in the same plane as the axis of the bar and is formed by the wings 40 and 4| which extend on either side from the neck portion down the sides of the center portion to a point below the center of the axis of the bar and preferably also the center of the aperture 38. The wings are spaced from the sides of the center portion and extend substantially parallel thereto to provide space between the wings and the center portion for the cover plates 29 and 30.

As far as I am aware, conventional rheostats were provided heretofore with sliders permitting of application of force for moving the sliders only at a point above the bar. In Fig. 1 such force is indicated by a dotted arrow 2. An application of force such as at 2 will evidently result in a tilting of the slider in the direction of the arrow 3 thus moving the brushes (in the illustrated embodiment 33) to the right. This tilting occurs particularly since the aperture in the slider through which the bar passes is larger than the cross-section of the bar to accommodate the second set of brushes for the bar.

Such tilting of the slider is undersirable as hereinbefore set forth since it leads to a change in the adjustment of the rheostat. When the force 2 ceases and the slider tilts back into its normal position, the previous adjustment of the rheostat is disturbed.

Tilting is further objectionable because it will considerably increase the friction between the slider and the bar resulting in many instances in jamming so that the slider becomes immovable. The novel form of slider permits of application of forc substantially in the axis of the bar 25 by providing finger operable grip portions substantially in the same plane as the axis of the bar 25. An application of force at the finger operable grip portion is indicated by the dotted arrow 4 and will result in a translatory movement of the slider without tilting.

Obviously the present invention is not restricted to the illustrated mbodiment but other forms of sliders and enclosures for the rheostat may conveniently be designed without departing from the spirit of the invention.

What is claimed is:

l. A rheostat comprising, in combination, a pair of end supports; a substantially cylindrical resistance element mounted therebetween, a bar mounted parallel to said element; an enclosure enclosing said element and bar forming with said supports a protective casing for said element and bar, said enclosure having a slot at the top above the said bar; a slider movable on said bar, said slider having a center portion with an aperture for accommodating said bar, a neck portion extending from said center portion through said slot and a finger operable portion extending from said neck portion downwardly on both sides, outwardly of said enclosure, into the plane of said bar; and a brush mounted on said center portion for engaging said element, whereby a force exerted at said finger operable portion in a direction substantially parallel to said bar will cause the slider and brush to move along the bar without tilting or jamming.

2. A rheostat comprising, in combination, a substantially cylindrical resistance element; a bar mounted parallel to said element; a slider movable on said bar, said slider having a center portion with an aperture for accommodating said bar, a narrow neck portion extending from said center portion, and a finger operable portion in the form of a pair of wings extending from said neck portion downwardly on either side and far enough as to provide a grip portion on either side and in the same plane as said bar; a brush assembly mounted on said center portion to make sliding contact with said element and said bar; and a protective casing enclosing said element, bar and center portion, said casing extending into the space of the slider between said wings and said center portion and having a slot for said neck portion to pass therethrough, whereby said rheostat is protected against human contact and a force exerted at said finger operable portion in a direction substantially parallel to said bar will cause the slider and brush to move along the bar without tilting or amming.

3. A rheostat comprising, in combination, a substantially cylindrical resistance element; a bar mounted parallel to said element; a slider movable on said bar said slider having a center portion with an aperture for accommodating said bar, a narrow neck portion extending from said center portion, and a finger operable portion in the form of a pair of wings extending from said neck portion downwardly on either side and far enough as to provide a grip portion on either side and in the same plane as said bar; a brush assembly mounted on said center portion to make sliding contact with said element and said bar; and a protective casing enclosing said element, bar and center portion, said casing comprising two end pieces supporting said element and bar and two side pieces fitting against said end pieces, extending into the space between the wings and the center portion of slider and forming a slot at the top adjacent to said neck portion of the slider through which said neck portion extends, whereby said rheostat is protected against human contact and a force exerted at said finger operable portion in a direction substantially parallel to said bar will cause the slider and brush to move along the bar without tilting or jamming. 4. As an article of manufacture a slider for rheostats equipped with an enclosing casing, said slider comprising a center portion having an aperture for accommodating a slider supporting bar; a neck portion extending from said center portion above said center portion, the neck portion being narrower than the center portion; and a finger operable portion in the form of a pair of wings extending on either side from the neck portion down the sides of the center portion to a point below the center of said aperture, the wings being spaced from the sides of the center portion and substantially parallel thereto and providing a finger grip portion at which an applied force will be directed substantially through the center of said aperture, the space between said wings and center portion extending to either side of the neck portion above said aperture. ROBERT ABRAHAMSON. 

